The biologic actions of parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) are mediated through a common PTH/PTHrP receptor. Down-regulation and desensitization of the PTH/PTHrP receptor is an important process in PTH/PTHrP receptor physiology. Binding of PTH or PTHrP to its receptor results in receptor phosphorylation, internalization, desensitization, recycling and or degradation. Internalization of the PTH/PTHrP receptor may lead to desensitization and/or re-sensitization of the PTH and PTHrP responses and/or downregulation and degradation of the receptor. In this project I will use cell lines, stably expressing a green fluorescent protein (GFP) tagged PTH/PTHrP receptor, to examine the hypotheses that 1) activation of the PTH/PTHrP receptor is required for internalization, 2) PTH-induced phosphorylation is required for internalization and 3) that internalization may have an important role in PTH/PTHrP receptor signaling through adenylate cyclase, phospholipase C, calcium and/or MAP kinase.